UDP glucose pyrophosphorylase (EC 2.7.7.9) is also called UTP-glucose-1-phosphate uridylyltransferase or glucose-1-phosphate uridylyltransferase. It catalyzes the interconversion of G-1-P and UDP-Glucose important in starch, pectin, and hemicellulose biosynthesis. UDP glucose pyrophosphorylasecatalyzes a phosphoanhydride exchange reaction in which the phosphoryl oxygen from glucose 1-phosphate attacks the alpha phosphorus atom from UTP to form UDP glucose and release pyrophosphate which is rapidly hydrolyzed. At least two mRNA populations of UDP-glucose pyrophosphorylase are present in most European potato cultivars. These isozymes are highly active and appear to be dimeric in nature. The two cDNA populations are related to a potato cultivar's ability to resist sweetening when exposed to cold temperatures (Sowokinos et al. (1997) Plant Physiol. 113:511-517). UDP-glucose pyrophosphorylase mRNA levels are reduced in response to “long term” stomatal opening and closing responses to environmental stress caused in planta by withholding water over a period of 2-4 days (Kopka et al. (1997) Plant J. 11:871-882).